Recently, along with the explosive increase of the amount of information and data handled by companies and governments, the capacity of data to be processed and stored in large-scale computers such as host computers or in storage sub-systems coupled to servers and host computers have increased rapidly. Especially, unlike servers and other information processing systems, storage sub-systems are specialized in storing data, utilizing a large number of hard disks as data memory media having large capacity and high reliability, and are managed and operated via a RAID (Redundancy Array of Inexpensive Disks) configuration.
The prices of storage sub-systems are being reduced recently, along with which the hard disk drives (hereinafter abbreviated as HDD) used in storage sub-systems conventionally adopting fiber channel (hereinafter abbreviated as FC) type devices, which are expensive and have extremely high reliability, are now adopting inexpensive SAS (Serial Attached SCSI) type devices, and are further adopting SATA (Serial AT Attachment) type devices which are even more inexpensive than SAS.
Moreover, the capacity of the HDD is increasing significantly due to the recent advancement in the art of high density recording. Therefore, the risk of increase of the frequency of occurrence of unrecoverable errors and recoverable errors caused by physical defects such as scratches formed on the media being the recording section of the HDD (due to defects during manufacture or scratches formed by head contact) or read failure caused by insufficient recording is anticipated, and in the worst case, the HDD may fail and must be replaced.
Patent literature 1 teaches an example of a replacement method for replacing such failure HDD. According to the disclosure, the storage sub-system monitors a failure that may occur in one data disk out of a plurality of data disks constituting one or more RAID groups. If the occurrence of failure of a data disk is detected, other data disks belonging to the same RAID group the data disk in which failure has occurred is used to perform correction copy to an arbitrary spare disk. Thereafter, when the data disk in which failure has occurred is replaced with a new data disk for replacement, the disk array system changes the management information so that the spare disk is managed as data disk and the data disk is managed as spare disk.